Indoor air treatment of formaldehyde by N-enriched activated carbon beads with or without CuO/Cu supported nanoparticles

Abstract

Activated carbon beads, either with or without copper-based nanoparticles, were prepared using an original method involving the impregnation of a chitosan hydrogel with KOH or NH₃, followed by thermochemical activation at temperatures between 500°C and 900°C. Elemental analysis and X-ray photoelectron spectroscopy indicate successful surface N-enrichment. The specific surface areas of the microporous beads ranged from 370 to 1330 m².g⁻¹. NH₃-activated carbons were shown to have a lower affinity for water vapor than KOH-activated carbons. Breakthrough curves for formaldehyde removal were investigated at an indoor air concentration of 850 ppbv and various humidities (0–50 % RH). High formaldehyde removal was found at RH = 50 % (43 mg.g⁻¹) for the NH₃-activated carbon, which is attributed to the presence of ultramicropores and nitrogen functional groups on its surface, such as pyrrolic groups. Well-dispersed aggregates of Cu and CuO nanoparticles were evidenced in the decorated beads using SEM and micro-tomography. In these novel materials, the nanoparticles can catalyse the degradation of formaldehyde into CO₂ and H₂O regardless of the relative humidity tested. Maximum degradation was reached at RH = 20 %. These innovative adsorbents and catalytic materials can degrade formaldehyde under indoor air conditions (25°C and humid air), suggesting promising applications in indoor air purification.